1. Field of the Invention
The present invention relates to improved poly(vinyl chloride)/polyamide multi-layer structures.
2. Description of the Prior Art
Electrical conductors typically consist of a wire conductor which is surrounded by a multi-layer structure. For example, see U.S. Pat. Nos. 3,576,940; 3,860,686; 4,079,191; 4,292,463; 4,327,248; 4,419,538; 4,472,597; 4,510,348; 4,626,619; and 4,691,082. Electrical conductors having a multi-layer structure of an inner layer of poly(vinyl chloride) (hereinafter PVC) and an outer layer of polyamide are taught in Japanese Patent 59146105, British Pat. No. 1257810, and Dutch Patent 6917475.
Although electrical conductors having an outer layer of polyamide perform well, a problem exists if the electrical conductor is stored outside and exposed to rain and high humidity. Upon contact with water, the polyamide layer tends to absorb moisture and expand considerably. This expansion causes the polyamide layer to swell away from the PVC layer and wrinkle. When the electrical conductor is then fed through a conduit, the wrinkled polyamide layer tears and is unacceptable for use in its intended purpose.
It would be desirable to have a multi-layer structure where good adhesion exists between the PVC layer and the polyamide layer. Multi-layer structures having a PVC layer, an adhesive layer, and a polyamide layer are known. Japanese Patent 62041039 teaches an adhesive layer comprising an acid-modified olefinic polymer and an acid-modified halogen-containing olefinic polymer. German Patent 1669973 teaches an adhesive layer having: (1) a primer layer comprising a mixture of epoxide compounds, hardener, and solvent, and (2) an epoxy adhesive layer.
It would be desirable to have a multi-layer structure, and more specifically, an electrical conductor where good adhesion exists, especially after the polyamide layer absorbs moisture, between the PVC layer and the polyamide layer.